The present invention relates to a technique of reducing noise in a semiconductor integrated circuit device and, particularly, to a technique effectively applied to reducing noise of low frequency band generated through DC fluctuations in a logic circuit.
As semiconductor devices are miniaturized, high integration and high-speed processing of semiconductor integrated circuit devices are more and more progressing and there is the trend to increase in consumed currents with the progression. For example, according to the International Semiconductor Technology Roadmap of 1999, there is a possibility that the operating frequency of high performance MPUs will become 6.7 times and the consumed currents 5.2 times more than those in the coming 10 years. Meanwhile, there is a possibility that supply voltages will become approximately ⅓ as much as the present ones because cuts in the supply voltages advance for restricting power consumption.
Now, the supply noise in the semiconductor circuit integrated device is roughly divided into a high frequency band and a low frequency band. The noise of the high frequency band is generated, due to a leak current momentarily flowing through a logic gate of the semiconductor integrated circuit device when the logic gate is operated synchronously with internal clock signals.
The magnitude of the noise of the high frequency band is obtained, by dividing a time-integrated value of AC fluctuation of the consumed currents in the semiconductor integral circuit device by a supply capacitor within a semiconductor chip. As noted above, although the consumed currents of the semiconductor integrated circuit device is probably increased, the noise of the high frequency band can be kept substantially constant by utilizing unused transistor regions or the like in the semiconductor chip and increasing the supply capacitor.
The noise of the low frequency band is also generated, due to resonance phenomena caused by the inductance of a package and the supply capacitor in the semiconductor chip. The magnitude thereof is proportional to DC fluctuations in the consumed current of the semiconductor integrated circuit device and the characteristic impedance of power source.
To reduce the noise of the low frequency band, it is necessary to take measures, such as reduction in the characteristic impedance of the power supply (for example, see Patent Document 1). However, the noise of the low frequency band is out of the question since the magnitude thereof is extremely small as compared to that of the high frequency band.
[Patent Document 1]
Japanese Patent Laid-open No. 11-150469